I posted this on the SA forums but I'll post it here as well. I was using 33d for this, but unless it's been fixed by "Made veins and other rock types collapse downward properly" I imagine it's still there. Anyway it's more like a whole panoply of issues all stacking up.
Ok so I generated a new world and found a glacier with a magma pipe. (It was Mirthful and the region name was awesome - The Helpful Cheerful Ice.) I staked out a 3x3 area on the local map (completely flat) and for the first time ever my FPS got above 40. My plan was to dig a large room in the rock for a farm, then carve out a couple layers overhead and drop a big cube of ice down onto the farm. Then the ice was supposed to melt and I could build my farm. Here's a side view of the planned situation.
code:
I=ice R=rock1 IIIIIIIIIIIIIIIIIIIII
2 IIIIII IIIIIII <--mined
3 IIIIII IIIIII IIIIIII <--mined and channeled except for the block of ice
4 III IIII <--this floor's been mined and channeled
5 RRR RRRR <--farm's on this level
6 RRRRRRRRRRRRRRRRRRRRR
I prepared a block of ice 1/7 the size of my farm and set things up as you see above. Then I went to level 2 and channeled out all the squares around where the block was. My ice cube thus was made up of the floor of level 2 and the walls and floor of level 3.
I couldn't stop my miner from channeling out the last connecting piece while he was on top of the ice block, but I thought he might be safe because he was on top of the whole thing.
Not a chance in hell.
The ice block fell all the way to the bottom in one step. But after that, I got a ton of "A section of your cavern has collapsed" messages, one each step. I think I got around 70 of them. The ice was shedding water everywhere and evidently bouncing back up to the very ceiling of the 4-story-high shaft at the same time. Or perhaps, water was somehow being thrown up into the ice layers and then refrozen, and then falling back down to the farm layers. This second theory is supported by the fact that my miner was immediately encased in ice, because when the game told me of his death it zoomed to level _4_ not 5. I guess a splash of water came up from the melting cube on level 5 and froze poor old Thod even as he was standing on top of the ice.
But here's the strange part. After everything had settled down, there was ice hanging from the top of the shaft. I'll try to draw a picture.
code:
I=ice R=rock w=water (1/7)1 IIIIIIIIIIIIIIIIIIIII
2 IIIIII I I IIIIIII
3 IIIIII III I IIIIIII
4 III I III III
5 RRRwwwwwwwwwwwwwwwRRR
6 RRRRRRR?
??RRRRRRRR
I don't know how ice walls managed to reform on level 2, which was above the original height of the ice block and which I had mined out completely beforehand. I checked the configuration of the ice on each level and indeed it was structurally sound by DF's standards - each piece was connected somehow to the ceiling.
But it gets even weirder. On levels 2 and 3, there were some raw chunks of "water" (the ice you get from mining ice walls) sitting on top of the ice. But there were also some on top of what the game assured me was open space. Also, the entire floor of level 5 beneath where the ice fell was demolished. But the rock on level 6 was still there. (The ???s on my diagram show the relevant area.) The "open space" tiles on floor five were covered with water (1/7) just like the rest of the farm, but when it drained away, I saw a tile I had never seen before. The game calls it "open space" but instead of showing a small dot the color of the rock one level beneath in the middle of black, it now shows a black dot in the middle of a tile the color of the rock underneath. The level 6 rock was revealed just as if I had built downward stairways on the tiles above. Needless to say I couldn't build farms on top of these spaces.
I have a save right after this happened if anybody wants to see it.
